Shoot Growth, Phosphorus–Nitrogen Relationships, and Yield of Canola in Response to Mineral Phosphorus Fertilization.

Bélanger, G., Ziadi, N., Pageau, D., Grant, C.A., Lafond, J., and Nyiraneza, J. (2015). "Shoot Growth, Phosphorus–Nitrogen Relationships, and Yield of Canola in Response to Mineral Phosphorus Fertilization.", Agronomy Journal, 107(4), pp. 1458-1464. doi : 10.2134/agronj15.0050  Access to full text

Abstract

Crop responses to increasing P fertilization are often variable and poorly related to soil P test. Our objectives were to determine the influence of P fertilizer on the growth and seed yield of canola (Brassica napus L.) and to develop a first approximation of its critical phosphorus concentration (Pc) in shoot biomass. An experiment with four rates of P fertilizer (0, 20, 40, and 80 kg P ha-1) was conducted on soils with a low available P content at 5 site-years [Normandin (QC; 2010, 2011, 2012) and Brandon (MB; 2010, 2012)] in Canada. Dry matter (DM) yield, and N and P concentrations were measured weekly on 5 d from early bolting to late flowering, and seed yield was measured at harvest. Seed yield was significantly increased by P fertilization at only 1 of the 5 site-years, even though a positive response was expected at all site-years. Phosphorus fertilization did not affect shoot growth and P uptake at any of the 5 site-years. However, the estimated shoot biomass on the first sampling day was reduced with no P application at 3 of the 5 site-years. A reduction in early crop growth of more than 30%, however, was required to affect seed yield. The whole-plant canola Pc was expressed as function of N concentration (Pc = 1.74 + 0.024N, R2 = 0.24, P = 0.05) but this first approximation requires further validation.

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